According to a mechanical device driven by a motor connected thereto, there are some cases where characteristics of the mechanical device including a motor control system appear in operation signals such as the rotation position, the speed, the torque of the motor, and the like. A motor control device having a function of extracting such characteristics from the operation signals and outputting the characteristics has been also proposed.
For example, when a motor that drives a mechanical device is feedback-controlled, in order to increase the responsiveness of the mechanical device, it is necessary to set a feedback gain to be large. However, when the feedback gain is too large at the time of a start-up adjustment of the mechanical device, signal components corresponding to high-frequency mechanical-resonance characteristics are excited. Consequently, a drive command (a torque command, for example) to the motor becomes vibrational and thus an operation of the mechanical device becomes vibrational.
Such a vibration is caused by a degradation in stability of a feedback control system. That is, as an index of the stability of a control system, a high-frequency vibration that appears in a drive command can be used. Here, a method has been proposed. That is, while a vibration state of a drive command to a motor is monitored, the responsiveness of a mechanical device is increased and a feedback gain is adjusted so as not to degrade the stability of the control system (see, for example, Patent Literature 1).
Patent Literature 1 discloses the invention that includes a unit of detecting a vibration when a motor is stopped at a position where an adjustment is performed to adjust a feedback gain at a plurality of positions in a movable range of a machine.
As another example of using a high-frequency vibration, a technique of detecting a high-frequency oscillation to safely stop a motor has been proposed (see, for example, Patent Literature 2). Patent Literature 2 discloses the invention that includes a unit of blocking control of a motor and a current command signal when an oscillation state of the motor is detected.